The present disclosure relates generally to power distribution systems. More particularly, the present disclosure relates to protection systems for power distribution systems.
Industrial power distribution systems commonly divide incoming power into a number of branch circuits. The branch circuits supply power to various equipment (i.e., loads) in the industrial facility. Circuit breakers are typically provided in each branch circuit to facilitate protecting equipment within the branch circuit. Circuit breakers are designed to open and close a circuit by non-automatic means and to open the circuit automatically on a predetermined over-current without damage to itself when properly applied within its rating. Since this automatic protection is based on conditions of the power (e.g., current), suppliers of circuit breakers have commonly made a large range circuit breakers to meet the various current demands, which can create inventory problems.
The inventory issue is made even more complex by the supplementary protectors that are often enclosed within the molded body of the circuit breaker. One common type of supplementary protector is known as an electronic trip unit. Electronic trip units typically include an analog-to-digital converter and a microprocessor. The electronic trip units receive signals from one or more sensors, such as, current transformers (CT's) and/or potential transformers (PT's). The sensors monitor a condition of the incoming power and provide an analog signal of the condition to the analog-to-digital converter. The A/D converter converts the analog signals from the sensors into digital signals, and provides the digital signals to the microprocessor. The microprocessor operates one or more control algorithms that provide the desired protection, monitoring, and control features.
The cost of each circuit breaker increases as the processing power of each microprocessor in its electronic trip unit increases. Namely, the cost of each circuit breaker increases as the complexity and number of protection features in the electronic trip unit is increased. Accordingly, suppliers of circuit breakers have also commonly manufactured a large range electronic trip units in the circuit breakers to meet the various consumer performance and price demands.
The large number of circuit breaker/trip unit combinations also adds cost and delay to the design and installation of the power distribution system. Moreover, it can increase the cost and delay associated with upgrading existing systems.
Accordingly, there is a continuing need for power distribution systems having low cost, easy to install components that provide the desired increased protection systems. It is also desired for such low cost components to ensure basic over-current protection in the event that other aspects of the protection fail.